Guanine Nucleotide Exchange Factor Activity Research Articles

Synthesis and Biochemical Evaluation of Noncyclic Nucleotide Exchange Proteins Directly Activated by cAMP 1 (EPAC1) Regulators.

Exchange proteins directly activated by cAMP (EPAC) play a central role in various biological functions, and activation of the EPAC1 protein has shown potential benefits for the treatment of various human diseases. Herein, we report the synthesis and biochemical evaluation of a series of noncyclic nucleotide EPAC1 activators. Several potent EPAC1 binders were identified including 25g, 25q, 25n, 25u, 25e, and 25f, which promote EPAC1 guanine nucleotide exchange factor activity in vitro. These agonists can also activate EPAC1 protein in cells, where they exhibit excellent selectivity toward EPAC over protein kinase A and G protein-coupled receptors. Moreover, 25e, 25f, 25n, and 25u exhibited improved selectivity toward activation of EPAC1 over EPAC2 in cells. Of these, 25u was found to robustly inhibit IL-6-activated signal transducer and activator of transcription 3 (STAT3) and subsequent induction of the pro-inflammatory vascular cell adhesion molecule 1 (VCAM1) cell-adhesion protein. These novel EPAC1 activators may therefore act as useful pharmacological tools for elucidation of EPAC function and promising drug leads for the treatment of relevant human diseases.

Mutations in SPATA13/ASEF2 cause primary angle closure glaucoma.

Current estimates suggest 50% of glaucoma blindness worldwide is caused by primary angle-closure glaucoma (PACG) but the causative gene is not known. We used genetic linkage and whole genome sequencing to identify Spermatogenesis Associated Protein 13, SPATA13 (NM_001166271; NP_001159743, SPATA13 isoform I), also known as ASEF2 (Adenomatous polyposis coli-stimulated guanine nucleotide exchange factor 2), as the causal gene for PACG in a large seven-generation white British family showing variable expression and incomplete penetrance. The 9 bp deletion, c.1432_1440del; p.478_480del was present in all affected individuals with angle-closure disease. We show ubiquitous expression of this transcript in cell lines derived from human tissues and in iris, retina, retinal pigment and ciliary epithelia, cornea and lens. We also identified eight additional mutations in SPATA13 in a cohort of 189 unrelated PACS/PAC/PACG samples. This gene encodes a 1277 residue protein which localises to the nucleus with partial co-localisation with nuclear speckles. In cells undergoing mitosis SPATA13 isoform I becomes part of the kinetochore complex co-localising with two kinetochore markers, polo like kinase 1 (PLK-1) and centrosome-associated protein E (CENP-E). The 9 bp deletion reported in this study increases the RAC1-dependent guanine nucleotide exchange factors (GEF) activity. The increase in GEF activity was also observed in three other variants identified in this study. Taken together, our data suggest that SPATA13 is involved in the regulation of mitosis and the mutations dysregulate GEF activity affecting homeostasis in tissues where it is highly expressed, influencing PACG pathogenesis.

Altered oligomeric states in pathogenic ALS2 variants associated with juvenile motor neuron diseases cause loss of ALS2‐mediated endosomal function

ALS2, the causative gene product for a number of recessive motor neuron diseases, forms a homophilic oligomer and acts as a guanine nucleotide exchange factor (GEF) for the small GTPase Rab5. This oligomerization is crucial for both Rab5 activation and ALS2‐mediated endosome fusion and maturation in cells. Recently, we have shown that pathogenic missense ALS2 variants retaining the Rab5 GEF activity fail to properly localize to endosomes via Rac1‐stimulated macropinocytosis. However, the molecular mechanisms underlying dysregulated distribution of ALS2 variants still unknown. In this study, we clarify the relationship between intracellular localization and oligomeric states of pathogenic ALS2 variants. Upon Rac1 activation, all variants moved from the cytosol to membrane ruffles, but not to macropinosomes and/or endosomes. Further, most wild‐type ALS2 in cultured cells forms tetramers. Importantly, the sizes of an ALS2 complex carrying missense mutations in the N‐terminus of RLD or in‐frame amino acid deletion in the PH domain were shifted toward high molecular weight, whereas the C‐terminal VPS9 domain missense mutant existed as a smaller dimeric or trimeric smaller form. Furthermore, in silico mutagenesis analyses using the RLD protein structure in conjunction with a cycloheximide chase assay in vitro disclosed that these missense mutations led to decrease in the protein stability. These results suggested that disorganized higher structures of ALS2 variants might explain their impaired endosomal localization and the stability, leading to loss of the ALS2 function. Currently, to further clarify the in vivo structure, gel‐filtration analyses of the ALS2 complex in murine tissues, including the brain, spinal cord and liver, are underway.Support or Funding InformationThis work was supported by Japanese Society for Promotion of Science Grants 26290018 and 24650189 and in part by the National Natural Science Foundation of China and JSPS Bilateral Joint Research Project.

PI3KC3 complex subunit NRBF2 is required for apoptotic cell clearance to restrict intestinal inflammation

ABSTRACT NRBF2, a regulatory subunit of the ATG14-BECN1/Beclin 1-PIK3C3/VPS34 complex, positively regulates macroautophagy/autophagy. In this study, we report that NRBF2 is required for the clearance of apoptotic cells and alleviation of inflammation during colitis in mice. NRBF2-deficient mice displayed much more severe colitis symptoms after the administration of ulcerative colitis inducer, dextran sulfate sodium salt (DSS), accompanied by prominent intestinal inflammation and apoptotic cell accumulation. Interestingly, we found that nrbf2 −/- mice and macrophages displayed impaired apoptotic cell clearance capability, while adoptive transfer of nrbf2 +/+ macrophages to nrbf2 −/- mice alleviated DSS-induced colitis lesions. Mechanistically, NRBF2 is required for the generation of the active form of RAB7 to promote the fusion between phagosomes containing engulfed apoptotic cells and lysosomes via interacting with the MON1-CCZ1 complex and regulating the guanine nucleotide exchange factor (GEF) activity of the complex. Evidence from clinical samples further reveals the physiological role of NRBF2 in maintaining intestinal homeostasis. In biopsies of UC patient colon, we observed upregulated NRBF2 in the colon macrophages and the engulfment of apoptotic cells by NRBF2-positive cells, suggesting a potential protective role for NRBF2 in UC. To confirm the relationship between apoptotic cell clearance and IBD development, we compared TUNEL-stained cell counts in the UC with UC severity (Mayo Score) and observed a strong correlation between the two indexes, indicating that apoptotic cell population in colon tissue correlates with UC severity. The findings of our study reveal a novel role for NRBF2 in regulating apoptotic cell clearance to restrict intestinal inflammation. Abbreviation: ANOVA: analysis of variance; ATG14: autophagy related 14; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); BMDM: bone marrow-derived macrophage; BSA: bovine serum albumin; CD: Crohn disease; CD68: CD68 molecule; CFP: cyan fluorescent protein; CMFDA: 5-chloromethylfluorescein diacetate; Co-IP, co-immunoprecipitation; CPR: C-reactive protein; Cy7: cyanine 7 maleimide; DAB: diaminobezidine 3; DAI: disease activity indexes; DAPI: 4ʹ6-diamidino-2-phenylindole; DMEM: dulbecco’s modified eagle’s medium; DMSO: dimethyl sulfoxide; DOC: sodium deoxycholate; DSS: dextran sulfate sodium; EDTA: ethylenediaminetetraacetic acid; EGTA: ethylenebis (oxyethylenenitrilo) tetraacetic acid; FBS: fetal bovine serum; FITC: fluorescein isothiocyanate; FRET: Förster resonance energy transfer; GDP: guanine dinucleotide phosphate; GEF: guanine nucleotide exchange factor; GFP: green fluorescent protein; GTP: guanine trinucleotide phosphate; GWAS: genome-wide association studies; HEK293: human embryonic kidney 293 cells; HRP: horseradish peroxidase; IBD: inflammatory bowel disease; IgG: immunoglobin G; IL1B/IL-1β: interleukin 1 beta; IL6: interleukin 6; IRGM: immunity related GTPase M; ITGAM/CD11b: integrin subunit alpha M; KO: knockout; LRRK2: leucine rich repeat kinase 2; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; MPO: myeloperoxidase; NaCl: sodium chloride; NEU: neutrophil; NOD2: nucleotide binding oligomerization domain containing 2; NP40: nonidet-P40; NRBF2: nuclear receptor binding factor 2; PBS: phosphate buffer saline; PCR: polymerase chain reaction; PE: P-phycoerythrin; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3P: phosphatidylinositol-3-phosphate; PTPRC/CD45: protein tyrosine phosphatase receptor type C; SDS-PAGE: sodium dodecylsulphate-polyacrylamide gel electrophoresis; TBST: tris-buffered saline Tween-20; Tris-HCl: trihydroxymethyl aminomethane hydrochloride; TUNEL: TdT-mediated dUTP nick-end labeling; UC: ulcerative colitis; ULK1: unc-51 like autophagy activating kinase 1; WB: western blotting; WT: wild type; YFP: yellow fluorescent protein.

Rab35–GEFs, DENND1A and folliculin differentially regulate podocalyxin trafficking in two- and three-dimensional epithelial cell cultures

Polarized epithelial cells have functionally distinct apical and basolateral membranes through which they communicate with external and internal bodily environments, respectively. The establishment and maintenance of this asymmetric structure depend on polarized trafficking of specific cargos, but the precise molecular mechanism is incompletely understood. We previously showed that Rab35, a member of the Rab family small GTPases, differentially regulates the trafficking of an apical cargo, podocalyxin (PODXL), in two-dimensional (2D) and three-dimensional (3D) Madin-Darby canine kidney (MDCK) II cell cultures through specific interactions with two distinct effectors, OCRL inositol polyphosphate-5-phosphatase (OCRL) and ArfGAP with coiled-coil, ankyrin repeat and pleckstrin homology domains 2 (ACAP2), respectively. However, whether the upstream regulators of Rab35 also differ depending on the culture conditions remains completely unknown. Here, we investigated four known guanine nucleotide exchange factors (GEFs) of Rab35, namely DENN domain-containing 1A (DENND1A), DENND1B, DENND1C, and folliculin (FLCN), and demonstrate that DENND1A and FLCN exhibit distinct requirements for Rab35-dependent PODXL trafficking under the two culture conditions. In 3D cell cultures, only DENDN1A-knockout cysts exhibited the inverted localization of PODXL similar to that of Rab35-knockout cysts. Moreover, the DENN domain, harboring GEF activity toward Rab35, was required for proper PODXL trafficking to the apical membrane. By contrast, FLCN-knockdown cells specifically accumulated PODXL in actin-rich structures similar to the Rab35-knockdown cells in 2D cell cultures. Our findings indicate that two distinct functional cascades of Rab35, the FLCN-Rab35-OCRL and the DENND1A-Rab35-ACAP2 axes, regulate PODXL trafficking in 2D and 3D MDCK II cell cultures, respectively.

Structure of the G protein chaperone and guanine nucleotide exchange factor Ric-8A bound to G\u03b1i1

Ric-8A is a cytosolic Guanine Nucleotide exchange Factor (GEF) that activates heterotrimeric G protein alpha subunits (Gα) and serves as an essential Gα chaperone. Mechanisms by which Ric-8A catalyzes these activities, which are stimulated by Casein Kinase II phosphorylation, are unknown. We report the structure of the nanobody-stabilized complex of nucleotide-free Gα bound to phosphorylated Ric-8A at near atomic resolution by cryo-electron microscopy and X-ray crystallography. The mechanism of Ric-8A GEF activity differs considerably from that employed by G protein-coupled receptors at the plasma membrane. Ric-8A engages a specific conformation of Gα at multiple interfaces to form a complex that is stabilized by phosphorylation within a Ric-8A segment that connects two Gα binding sites. The C-terminus of Gα is ejected from its beta sheet core, thereby dismantling the GDP binding site. Ric-8A binds to the exposed Gα beta sheet and switch II to stabilize the nucleotide-free state of Gα.

TIAM2S as a novel regulator for serotonin level enhances brain plasticity and locomotion behavior.

TIAM2S, the short form of human T-cell lymphoma invasion and metastasis 2, can have oncogenic effects when aberrantly expressed in the liver or lungs. However, it is also abundant in healthy, non-neoplastic brain tissue, in which its primary function is still unknown. Here, we examined the neurobiological and behavioral significance of human TIAM2S using the human brain protein panels, a human NT2/D1-derived neuronal cell line model (NT2/N), and transgenic mice that overexpress human TIAM2S (TIAM2S-TG). Our data reveal that TIAM2S exists primarily in neurons of the restricted brain areas around the limbic system and in well-differentiated NT2/N cells. Functional studies revealed that TIAM2S has no guanine nucleotide exchange factor (GEF) activity and is mainly located in the nucleus. Furthermore, whole-transcriptome and enrichment analysis with total RNA sequencing revealed that TIAM2S-knockdown (TIAM2S-KD) was strongly associated with the cellular processes of the brain structural development and differentiation, serotonin-related signaling, and the diseases markers representing neurobehavioral developmental disorders. Moreover, TIAM2S-KD cells display decreased neurite outgrowth and reduced serotonin levels. Moreover, TIAM2S overexpressing TG mice show increased number and length of serotonergic fibers at early postnatal stage, results in higher serotonin levels at both the serum and brain regions, and higher neuroplasticity and hyperlocomotion in latter adulthood. Taken together, our results illustrate the non-oncogenic functions of human TIAM2S and demonstrate that TIAM2S is a novel regulator of serotonin level, brain neuroplasticity, and locomotion behavior.

A trimeric metazoan Rab7 GEF complex is crucial for endocytosis and scavenger function.

Endosome biogenesis in eukaryotic cells is critical for nutrient uptake and plasma membrane integrity. Early endosomes initially contain Rab5, which is replaced by Rab7 on late endosomes prior to their fusion with lysosomes. Recruitment of Rab7 to endosomes requires the Mon1-Ccz1 guanine-nucleotide-exchange factor (GEF). Here, we show that full function of the Drosophila Mon1-Ccz1 complex requires a third stoichiometric subunit, termed Bulli (encoded by CG8270). Bulli localises to Rab7-positive endosomes, in agreement with its function in the GEF complex. Using Drosophila nephrocytes as a model system, we observe that absence of Bulli results in (i) reduced endocytosis, (ii) Rab5 accumulation within non-acidified enlarged endosomes, (iii) defective Rab7 localisation and (iv) impaired endosomal maturation. Moreover, longevity of animals lacking bulli is affected. Both the Mon1-Ccz1 dimer and a Bulli-containing trimer display Rab7 GEF activity. In summary, this suggests a key role for Bulli in the Rab5 to Rab7 transition during endosomal maturation rather than a direct influence on the GEF activity of Mon1-Ccz1.

Deficiencies in vesicular transport mediated by TRAPPC4 are associated with severe syndromic intellectual disability.

The conserved transport protein particle (TRAPP) complexes regulate key trafficking events and are required for autophagy. TRAPPC4, like its yeast Trs23 orthologue, is a core component of the TRAPP complexes and one of the essential subunits for guanine nucleotide exchange factor activity for Rab1 GTPase. Pathogenic variants in specific TRAPP subunits are associated with neurological disorders. We undertook exome sequencing in three unrelated families of Caucasian, Turkish and French-Canadian ethnicities with seven affected children that showed features of early-onset seizures, developmental delay, microcephaly, sensorineural deafness, spastic quadriparesis and progressive cortical and cerebellar atrophy in an effort to determine the genetic aetiology underlying neurodevelopmental disorders. All seven affected subjects shared the same identical rare, homozygous, potentially pathogenic variant in a non-canonical, well-conserved splice site within TRAPPC4 (hg19:chr11:g.118890966A>G; TRAPPC4: NM_016146.5; c.454+3A>G). Single nucleotide polymorphism array analysis revealed there was no haplotype shared between the tested Turkish and Caucasian families suggestive of a variant hotspot region rather than a founder effect. In silico analysis predicted the variant to cause aberrant splicing. Consistent with this, experimental evidence showed both a reduction in full-length transcript levels and an increase in levels of a shorter transcript missing exon 3, suggestive of an incompletely penetrant splice defect. TRAPPC4 protein levels were significantly reduced whilst levels of other TRAPP complex subunits remained unaffected. Native polyacrylamide gel electrophoresis and size exclusion chromatography demonstrated a defect in TRAPP complex assembly and/or stability. Intracellular trafficking through the Golgi using the marker protein VSVG-GFP-ts045 demonstrated significantly delayed entry into and exit from the Golgi in fibroblasts derived from one of the affected subjects. Lentiviral expression of wild-type TRAPPC4 in these fibroblasts restored trafficking, suggesting that the trafficking defect was due to reduced TRAPPC4 levels. Consistent with the recent association of the TRAPP complex with autophagy, we found that the fibroblasts had a basal autophagy defect and a delay in autophagic flux, possibly due to unsealed autophagosomes. These results were validated using a yeast trs23 temperature sensitive variant that exhibits constitutive and stress-induced autophagic defects at permissive temperature and a secretory defect at restrictive temperature. In summary we provide strong evidence for pathogenicity of this variant in a member of the core TRAPP subunit, TRAPPC4 that associates with vesicular trafficking and autophagy defects. This is the first report of a TRAPPC4 variant, and our findings add to the growing number of TRAPP-associated neurological disorders.

The small GTPase Rab5a and its guanine nucleotide exchange factors are involved in post-Golgi trafficking of storage proteins in developing soybean cotyledon.

Storage protein is the most abundant nutritional component in soybean seed. Morphology-based evidence has verified that storage proteins are initially synthesized on the endoplasmic reticulum, and then follow the Golgi-mediated pathway to the protein storage vacuole. However, the molecular mechanisms of storage protein trafficking in soybean remain unknown. Here, we clone the soybean homologs of Rab5 and its guanine nucleotide exchange factor (GEF) VPS9. GEF activity combined with yeast two-hybrid assays demonstrated that GmVPS9a2 might specifically act as the GEF of the canonical Rab5, while GmVPS9b functions as a common activator for all Rab5s. Subcellular localization experiments showed that GmRab5a was dually localized to the trans-Golgi network and pre-vacuolar compartments in developing soybean cotyledon cells. Expression of a dominant negative variant of Rab5a, or RNAi of either Rab5a or GmVPS9s, significantly disrupted trafficking of mRFP-CT10, a cargo marker for storage protein sorting, to protein storage vacuoles in maturing soybean cotyledons. Together, our results systematically revealed the important role of GmRab5a and its GEFs in storage protein trafficking, and verified the transient expression system as an efficient approach for elucidating storage protein trafficking mechanisms in seed.

Comparative gene expression analysis of the engulfment and cell motility (ELMO) protein family in the mouse brain

Engulfment and cell motility (ELMO) proteins bind to Dock180, a guanine nucleotide exchange factor (GEF) of the Rac family, and regulate GEF activity. The resultant ELMO/Dock180/Rac module regulates cytoskeletal reorganization responsible for the engulfment of apoptotic cells, cell migration, and neurite extension. The expression and function of Elmo family proteins in the nervous system, however, are not yet fully understood. Here, we characterize the comparative gene expression profiles of three Elmo family members (Elmo1, Elmo2, and Elmo3) in the brain of C57BL/6J mice, a widely used inbred strain, together with reeler mutant mice to understand gene expression in normal laminated brain areas compared with abnormal areas. Although all three Elmo genes showed widespread mRNA expression over various mouse tissues tested, Elmo1 and Elmo2 were the major types expressed in the brain, and three Elmo genes were up-regulated between the first postnatal week (infant stage) and the third postnatal week (juvenile, weaning stage). In addition, the mRNAs of Elmo genes showed distinct distribution patterns in various brain areas and cell-types; such as neurons including inhibitory interneurons as well as some non-neuronal cells. In the cerebral cortex, the three Elmo genes were widely expressed over many cortical regions, but the predominant areas of Elmo1 and Elmo2 expression tended to be distributed unevenly in the deep (a lower part of the VI) and superficial (II/III) layers, respectively, which also changed depending on the cortical areas and postnatal stages. In the dentate gyrus of the hippocampus, Elmo2 was expressed in dentate granule cells more in the mature stage rather than the immature-differentiating stage. In the thalamus, Elmo1 but not the other members was highly expressed in many nuclei. In the medial habenula, Elmo2 and Elmo3 were expressed at intermediate levels. In the cerebellar cortex, Elmo1 and Elmo2 were expressed in differentiating-mature granule cells and mature granule cells, respectively. In the Purkinje cell layer, Elmo1 and Elmo2 were expressed in Purkinje cells and Bergmann glia, respectively. Disturbed cellular distributions and laminar structures caused by the reeler mutation did not severely change expression in these cell types despite the disturbed cellular distributions and laminar structures, including those of the cerebrum, hippocampus, and cerebellum. Taken together, these results suggested that these three Elmo family members share their functional roles in various brain regions during prenatal-postnatal development.

A Network Pharmacology Approach to Uncover the Molecular Targets and Associated Potential Pathways of Lycii Fructus for the Treatment of Retinitis Pigmentosa

ObjectiveTo explore the molecular targets and associated potential pathways of Lycii Fructus (LF, Gou Qi Zi, 枸杞子) in the treatment of retinitis pigmentosa (RP) by the approaches of network pharmacology and bioinformatics. MethodsThe potential blood-entry active ingredients and targets of LF were retrieved by Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP). RP-related gene targets were retrieved through disease comprehensive databases. Protein-protein interaction (PPI) network of LF component-targets and RP disease-targets was constructed by STRING, and the intersection of the 2 networks was extracted. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of theintersection network were conducted by Database for Annotation, Visualization and Integrated Discovery (DAVID). CytoHubba was used to screen the key targets. ResultsA total of 188 chemical constituents related to LF was retrieved from TCMSP database. 45 active ingredients were screened according to pharmacokinetic parameters oral bioavailability (OB) and drug similarity (DL). 36 active ingredients were further screened and 201 targets related to these constituents were obtained. 206 target genes directly related to RP were obtained from the disease comprehensive databases, and 89 genes were obtained from the intersection of component-target and disease-target PPI network. These genes were mainly involved in intracellular signal transduction, GTPase activity regulation, cell morphology regulation, and other biological processes. Molecular functions were mainly related to Rho guanine nucleotide exchange factor activity, GTPase activator activity, receptor signal protein serine/threonine kinase activity and so on. They were enriched in the cytoplasm, cell membrane, Golgi apparatus, and other regions. The mechanism was related to cell cycle pathways, neurotrophin signaling pathways, Ras signaling pathways, and so on. 10 key gene targets of LF in the treatment of RP were screened. ConclusionsThe material basis for LF to exert its pharmacodynamic effect is 36 active ingredients such as cycloartenol, mandenol, and so on. The key targets of LF in the treatment of RP include 10 genes, such as Rho, PAK, and so on. The main mechanism is related to the regulation of the Ras signaling pathway, neurotrophin signaling pathway, cell cycle related pathway, and other signaling networks.

Oxidized base 8-oxoguanine, a product of DNA repair processes, contributes to dendritic cell activation

A growing body of evidence suggests that elevated levels of reactive oxygen species (ROS) in the airways caused by exposure to gas phase pollutants or particulate matter are able to activate dendritic cells (DCs); however, the exact mechanisms are still unclear. When present in excess, ROS can modify macromolecules including DNA. One of the most abundant DNA base lesions is 7,8-dihydro-8-oxoguanine (8-oxoG), which is repaired by the 8-oxoguanine DNA glycosylase 1 (OGG1)-initiated base excision repair (BER) (OGG1-BER) pathway. Studies have also demonstrated that in addition to its role in repairing oxidized purines, OGG1 has guanine nucleotide exchange factor activity when bound to 8-oxoG. In the present study, we tested the hypothesis that exposure to 8-oxoG, the specific product of OGG1-BER, induces functional changes of DCs. Supporting our hypothesis, transcriptome analysis revealed that in mouse lungs, out of 95 genes associated with DCs’ function, 22 or 42 were significantly upregulated after a single or multiple intranasal 8-oxoG challenges, respectively. In a murine model of allergic airway inflammation, significantly increased serum levels of ovalbumin (OVA)-specific IgE antibodies were detected in mice sensitized via nasal challenges with OVA+8-oxoG compared to those challenged with OVA alone. Furthermore, exposure of primary human monocyte-derived DCs (moDC) to 8-oxoG base resulted in significantly enhanced expression of cell surface molecules (CD40, CD86, CD83, HLA-DQ) and augmented the secretion of pro-inflammatory mediators IL-6, TNF and IL-8, whereas it did not considerably influence the production of the anti-inflammatory cytokine IL-10. The stimulatory effects of 8-oxoG on human moDCs were abolished upon siRNA-mediated OGG1 depletion. Collectively, these data suggest that OGG1-BER-generated 8-oxoG base-driven cell signaling activates DCs, which may contribute to initiation of both the innate and adaptive immune responses under conditions of oxidative stress.

Abstract 4235: Phosphorylation of Serine 861 in the ECT2 guanine nucleotide exchange factor activates Rho family GTPases and is a biomarker for several tumor types

Abstract The Rho family of GTPases, which cycle between inactive GDP-bound and active GTP-bound states, have high activity in many cancers. One mechanism for their activation is by guanine nucleotide exchange factors (GEFs), which stimulate the replacement of GDP-bound Rho with GTP-bound Rho. In this study, we report phosphorylation of Epithelial Cell Transforming 2 (ECT2), which is a Rho family-specific GEF, is a biomarker in several tumor types, based on bioinformatic analysis and biological assays. Our analysis of the NCI Clinical Proteomic Tumor Analysis Consortium (CPTAC) database found that Serine 861 (S861) in ECT2 is more highly phosphorylated in several tumor types compared to its phosphorylation in the relevant normal tissue. S861 phosphorylation is 2.1-fold and 2.4-fold higher in colon cancer and ovarian cancer, respectively, and high S861 phosphorylation in breast cancer is correlated with a poorer prognosis. Phosphorylation of S861 is especially high in triple-negative breast cancer, as it is 2.3-fold higher in this type compared with the other types of breast cancer. Increased phosphorylation of S861 is associated increased ECT2 mRNA and protein levels in colon cancer and breast cancer. In experimental studies, siRNA knockdown of endogenous ECT2 in two triple-negative breast cancer lines resulted in lower levels of RhoA-GTP, Rac-GTP, and Cdc42-GTP, and led to reduced cell migration, cell proliferation, and anchorage-independent growth, suggesting that ECT2 is a key regulator of cellular signaling and oncogenic growth in the triple-negative lines. Conversely, ectopic expression of wild-type ECT2 induced increased levels of RhoA-GTP, Rac-GTP, and Cdc42-GTP and promoted migration, proliferation, and anchorage-independent growth. Compared with wild type ECT2, ectopic expression of ECT2 carrying a phospho-defective (S861A) or phospho-mimic (S861D) mutation, respectively, reduced or enhanced ECT2 GEF and biological activities. Our results indicate that phosphorylation of S861 enhances the pro-oncogenic activity of ECT2, which is correlated with the increased phosphorylation of S861 in the three cancer types, the increased expression of ECT2 in two of these cancer types, and the prognostic significance of S861 phosphorylation in breast cancer. * Dunrui Wang and Xiaolan Qian are Equal contributors Citation Format: Dunrui Wang, Xiaolan Qian, Sarah Eng, Shivani Nellore, Alex G. Papageorge, Douglas R. Lowy. Phosphorylation of Serine 861 in the ECT2 guanine nucleotide exchange factor activates Rho family GTPases and is a biomarker for several tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4235.

Structure, Function, and Dynamics of the Gα Binding Domain of Ric-8A

Ric-8A is a 530-amino acid cytoplasmic molecular chaperone and guanine nucleotide exchange factor (GEF) for i, q, and 12/13 classes of heterortrimeric G protein alpha subunits (Gα). We report the 2.2-Å crystal structure of the Ric-8A Gα-binding domain with GEF activity, residues 1-452, and is phosphorylated at Ser435 and Thr440. Residues 1-429 adopt a superhelical fold comprised of Armadillo (ARM) and HEAT repeats, and the C terminus is disordered. One of the phosphorylated residues potentially binds to a basic cluster in an ARM motif. Amino acid sequence conservation and published hydrogen-deuterium exchange data indicate repeats 3 through 6 to be a putative Gα-binding surface. Normal mode modeling of small-angle X-ray scattering data indicates that phosphorylation induces relative rotation between repeats 1-4, 5-6, and 7-9. 2D 1H-15N-TROSY spectra of [2H,15N]-labeled Gαi1 in the presence of R452 reveals chemical shift perturbations of the C terminus and Gαi1 residues involved in nucleotide binding.

Spatial control of the GTPase MglA by localized RomR–RomX GEF and MglB GAP activities enables Myxococcus xanthus motility

The rod-shaped Myxococcus xanthus cells move with defined front-rear polarity using polarized motility systems. A polarity module consisting of the small GTPase MglA, its cognate GTPase activating protein (GAP) MglB and RomR establishes this polarity. Agl-Glt gliding motility complexes assemble and disassemble at the leading and lagging pole, respectively. These processes are stimulated by MglA-GTP at the leading and MglB at the lagging pole. Here, we identify RomX as an integral component of the polarity module. RomX and RomR form a complex that has MglA guanine nucleotide exchange factor (GEF) activity and also binds MglA-GTP. In vivo RomR recruits RomX to the leading pole forming the RomR-RomX complex that stimulates MglA-GTP formation and binding, resulting in a high local concentration of MglA-GTP. The spatially separated and opposing activities of the RomR-RomX GEF at the leading and the MglB GAP at the lagging cell pole establish front-rear polarity by allowing the spatially separated assembly and disassembly of Agl-Glt motility complexes. Our findings uncover a regulatory system for bacterial cell polarity that incorporates a nucleotide exchange factor as well as an NTPase activating protein for regulation of a nucleotide-dependent molecular switch and demonstrate a spatial organization that is conserved in eukaryotes.

The biological function of naturally occurring DOCK2 inhibitor in tissue-specific immune evasion

Abstract Study objection DOCK2 is a Rac-specific guanine nucleotide exchange factor (GEF) predominantly expressed in hematopoietic cells. DOCK2 is essential for migration and activation of leukocytes, and its mutations in humans cause severe immunodeficiency, thereby indicating that DOCK2 plays a key role in immune surveillance. Interestingly, however, we found that a naturally occurring DOCK2 inhibitor exists in our body and named this molecule DOCK2 inhibitory metabolite (D2IM). In this study, we aimed to reveal biological functions of D2IM. Method The specificity of D2IM was examined with Rac GEF assay and binding assay. T cells and neutrophils from WT mouse were treated with D2IM and subjected to Rac activation assay and chemotaxis assay. D2IM production in various tissues was monitored with mass spectrometry. In addition, influence of the lack of CS on ultraviolet- and antigen-induced ocular inflammationwas analyzed using KO mice lacking D2IM synthase. Result CS inhibited the Rac GEF activity of murine DOCK2 protein in vitro with a IC50 value of 2.0 mM. When leukocytes were treated with D2IM, chemoattractant-induced Rac activation was severely impaired, resulting in a marked reduction of migratory response of lymphocytes and neutrophils. D2IM most abundantly existed in the Harderian gland, which produces lipids to form the oily layer of the tear film, and its production was completely lost in mice lacking D2IM synthase. We found that the lack of D2IM augmented ultraviolet- and antigen-induced ocular inflammation in mice, which was suppressed by administration of eye drops containing D2IM. Conclusion D2IM is a naturally occurring DOCK2 inhibitor that contributes to create immune evasive microenvironment in the eye.

Molecular Mechanism of Rap1A‐Dependent Activation of PLCɛ

Phospholipase C (PLC) enzymes hydrolyze phosphatidylinositol lipids to produce diacylglycerol (DAG) and inositol phosphates, leading to the activation of protein kinase C (PKC) and downstream signaling pathways, including cell growth and survival. The PLCɛ subfamily is a key player in cardiovascular function, where it contributes to maximum contractility. However, prolonged activation of PLCɛ results in cardiac hypertrophy and heart failure through its ability to regulate the expression of hypertrophic genes. This process is regulated by the small GTPase Rap1A, which is activated downstream of β‐adrenergic receptors. Rap1A binds to the C‐terminal Ras association (RA) domain of PLCɛ, simultaneously translocating the complex to the perinuclear region and activating PLCɛ. PLCɛ also contains an N‐terminal CDC25 domain, which has guanine nucleotide exchange factor (GEF) activity for Rap1A resulting in a feed forward activation loop and sustained lipid hydrolysis. However, the molecular mechanism of this process is not known. In this work, we seek to characterize the interactions between Rap1A and PLCɛ using structural and functional studies to map the Rap1A binding site on PLCɛ and determine whether activation results in conformational changes that release autoinhibition and/or increase membrane association. These studies provide the first molecular details of the Rap1A‐dependent activation of PLCɛ and open the door to the development of new therapeutic strategies for treating cardiac hypertrophy.Support or Funding InformationThis research is supported by the American Heart Association Predoctoral Fellowship 18PRE33990057 to M.S., American Heart Association Grant Scientist Development Grant 16SDG29920017 to A.M.L. and the NIH NLHBI 1R01HL 141076‐01 to A.M.L. SAXS data was collected and analyzed with the assistance of S. Chakravarthy at Argonne National Laboratory.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Structural Insights into Phospholipase Cɛ Function

Phospholipase Cɛ (PLCɛ) is a member of the PLC family of enzymes that hydrolyze phosphatidylinositol lipids downstream of G protein coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). PLCɛ is unique among the PLC superfamily as it contains an N‐terminal CDC25 domain, which has guanine nucleotide exchange factor (GEF) activity towards small G proteins Rap1A, and two C‐terminal Ras association (RA) domains. The best characterized pathway leading to PLCɛ activation is mediated through β‐adrenergic receptor (βARs) signaling. Stimulation of these receptors culminates in the activation of the small GTPase, Rap1A, which binds directly to PLCɛ and translocates the complex to the Golgi. There, PLCɛ hydrolyzes phosphatidylinol‐4‐phosphate (PI4P). Prolonged activation of this pathway results in increased expression of hypertrophy‐related genes. However, how the structural basis of PLCɛ activity under basal conditions and upon activation by Rap1A are unknown. Towards this end, we have obtained the first high‐resolution insights into a catalytically active PLCɛ variant. These studies, together with biochemical analysis of the intramolecular contacts observed in the structure, provide the first molecular insights into this enzyme.Support or Funding InformationThis research is supported by American Heart Association Scientist Development Grant 16SDG29920017 and NIH 1R01HL141076‐01 to A.M.LThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Structural basis of guanine nucleotide exchange for Rab11 by SH3BP5.

The Rab GTPase family is a major regulator of membrane traffic in eukaryotic cells. The Rab11 subfamily plays important roles in specific trafficking events such as exocytosis, endosomal recycling, and cytokinesis. SH3BP5 and SH3BP5-like (SH3BP5L) proteins have recently been found to serve as guanine nucleotide exchange factors (GEF) for Rab11. Here, we report the crystal structures of the SH3BP5 GEF domain alone and its complex with Rab11a. SH3BP5 exhibits a V-shaped structure comprising two coiled coils. The coiled coil composed of α1, and α4 is solely responsible for the Rab11a binding and GEF activity. SH3BP5 pulls out and deforms switch I of Rab11a so as to facilitate the GDP release from Rab11a. SH3BP5 interacts with the N-terminal region, switch I, interswitch, and switch II of Rab11a. SH3BP5 and SH3BP5L localize to Rab11-positive recycling endosomes and show GEF activity for all of the Rab11 family but not for Rab14. Fluorescence-based GEF assays combined with site-directed mutagenesis reveal the essential interactions between SH3BP5 and Rab11 family proteins for the GEF reaction on recycling endosomes.